1. Field of Invention
This invention relates to rack apparatus and, more particularly, to rack apparatus for wiring panels or printed circuit boards.
2. Description of the Prior Art
The terms "printed circuit boards" and "wiring panels" are substantially synonymous in meaning. The term "printed circuit board" is an older term, while the term "wiring panel" is a newer more contemporary, term. In the following specification, both terms may be used interchangeably.
In the fabrication of wiring panels or printed circuit boards, there may be a plurality of discrete panels or boards fabricated on a relatively large, composite circuit board blank. For example, a printed circuit board blank, having dimensions roughly 24 inches by 24 inches (70 cm .times.70 cm), may include four discrete printed circuit boards. After the completed processing of the composite board, the composite board will be cut into the four discrete printed circuit boards, each of which is roughly 1/4 the size of the entire, single, composite board.
Moreover, some printed circuit boards are relatively large even though they may include only a single circuit layout, rather than a plurality of discrete circuits.
The relatively large circuit boards provide some inherent problems in their processing that are not present in the processing of smaller boards. The lack of stiffness of the large printed circuit boards is the primary problem. The rack apparatus of the present invention overcomes the lack of stiffness problem.
In the processing of these relatively large printed circuit boards, the substrate board, with its etched circuits thereon, goes through different enchant baths and rinse baths. A plurality of the circuit boards is disposed in a single rack, and the rack is in turn handled by appropriate materials handling equipment for conveying, dipping, and lifting. Each rack is typically made of stainless steel so that it will not react with the acid baths, etc., into which the circuit boards are dipped during the processing stages or steps.
Each large printed circuit board is relatively flexible, and if adjacent boards contact each other, there may be, and usually are, resulting defects in the boards. Accordingly, it is necessary that the boards not contact each other and that they remain spaced apart from each other all during the processing steps.
In the prior art, the circuit board elements typically are held upright in a wire rack, and the likelihood of the adjacent boards touching or contacting each other or contacting the wire rack is relatively great. There is a reject rate of the boards that may be as high as 25 or 30 percent due to the touching or contacting problem.
The apparatus of the present invention prevents the contact between adjacent boards and substantially eliminates any part of the rack from being in the circuit board area by providing a curved rack, or curved guides in a rack, so that the printed circuit boards are arcuately curved during the processing. The arcuate curve in each board provides sufficient stiffening of the boards to prevent the undesirable contact between the adjacent boards during processing, transporting, etc. The boards contact the rack apparatus only at the outer periphery of the boards, where there are no circuit elements.
In addition to appropriately supporting the large circuit boards, the rack apparatus of the present invention includes sufficient open space to provide for the quick drain of the liquid materials into which the racks are lowered for the processing. This provides a minimal drag-out of the liquids. Obviously, the drag-out of the material is undesirable for several reasons. Among the reasons are the loss of the acid or other processing material and the dilution of the rinse material.